Priming pumps are known that are made of elastomer and that present an enclosure having a central zone that is elastically deformable between a rest state, in which the enclosure has a maximum volume, and a pressed state. The enclosure includes coupling zones at the inlet and the outlet of the central zone, which include check valves that are arranged so as to enable fluid to pass in a determined direction each time the enclosure is pressed.
Recent motor-vehicle engines (in particular diesel engines having a common injector unit) have the characteristic of working at a high average temperature, it being possible for the fuel to be raised to 125° Celsius (C) on a continuous basis, for example, with peaks of up to 150° C.
In addition, in the feed circuits provided for that type of engine, the priming pumps can be mounted in parallel with the injection pump on the feed circuit and are no longer in series with said feed circuit, such that the inside of the priming pump no longer has fuel flowing therethrough but, on the contrary, contains stagnant fuel.
It should be observed that under such conditions, the materials currently used for making enclosures tend to age prematurely for various reasons.
Firstly, the acidity that the fuel acquires at high temperatures, combined with the high amplitude of the temperature variations, causes the enclosure to deteriorate prematurely.
Secondly, the additives contained in the recent fuels provided for that type of engine are particularly corrosive for the material of the enclosure, especially at high temperature.
Furthermore, the stagnant fuel infiltrates naturally into the pores of the material of the enclosure, thereby leaching out the fillers included in the material to give it its elasticity.
In order to make a priming pump enclosure that satisfies such constraints, consideration has been given to using a material of the fluoroelastomer type, which withstands both chemical and thermal attacks and retains its elasticity over time. However, in addition to that material being too costly for it to be envisaged for use in the context of mass production, it is also difficult to recycle.